Apparatus for extraction by the double solvent method



Sept. 20, 196 T; MIGNONE 2,953,501

APPARATUS FOR EXTRACTION BY THE DOUBLE SOLVENT METHOD Filed Jan. 22,1958 APPARATUS FOR EXTRACTION BY THE DOUBLE SOLVENT METHOD TomasoMignone, Ravenna, Italy, assignor to S.A.R.O.M. Societa AzionariaRaflinazione Olii Minerali, Milan, Italy Filed Jan. 22, 1958, Ser. No.710,496

Claims priority, application Italy July 18, 1957 2 Claims. (Cl.196-1452) oils of which one component consists of paraflin oils and theother of aromatic i.e. non-paraffin oils. It is to be understood,however, that, selecting suitable solvents, the invention may also beapplied to other homogeneous mixtures (solutions) as for example amixture of acetoneacetic acid (using chloroform as a solvent for theacetone and water as a solvent for the acetic acid), or a mixture ofparachloronitrobenzol orthochloronitrobenzol (in which the first isdissolved with heptane and the latter with methane). This specification,however, is particularly concerned with mineral lubricating oils.

As is Well-known it is frequently necessary in the production oflubricating oils to separate the paraifin hydrocarbons from the aromaticand asphaltic hydrocarbons, and as the viscosity of the former is muchless afiected by temperature than is the case with the latter, paraflinoils present far superior properties as lubricants.

The term paraifin as used in this connection is not to be interpretedliterally, but is intended to imply a phase composed of hydrocarbons inwhich aliphatic chains largely preponderate; the same applies by analogyto the terms aromatic and asphaltic respectively.

The separation of a crude oil into its paralfin and non-parafiin phasesis effected industrially by means of solvent extraction operations. Alarge number of chemical'compounds are known to be suitable solvents,each nn'der certain conditions of application and for specific types ofoperations. Some of these solvents have a highly polar molecule e.g.phenol, cresols, furfural, sulphurous acid, nitrobenzol and aniline:these solvents present good solubility with non-parafiin hydrocarbons,but are barely soluble in parafiin hydrocarbons. A crude oil, if mixed;with one of these solvents, will separate out into a layer composed ofthe solvent with incorporated non-paraffin hydrocarbons, and a layercomposed of paraffin hydrocarbons containing a small quantity of thesolvent.

In the case of certain crude oils, e.g. all oils rich in -asphalticproducts and composed of vacuum distillation residues, treatment with asingle solvent (as referred to above) is no longer adequate, as it isfirst necessary to feliminatethe asphalt content of the oil. This isgenerally :done'by precipitating out the asphalt with a mixture ofliquefied propane and propylene. i

According to 'the method as practised at :the present time, a crude oilcontaining, asphaltic components is first jsubjectedto treatment withpropane toxremove the asphalt, and then to successive extraction withone of the solvents mentioned-abovefor the separation of the paraf- -finoils on the one hand, and of the aromatic 'oilson the other; As will beseen in the following, the yields result ingfrom such a process areunsatisfactory, and one'of the principal purposes of this invention istoprovide a process and apparatus afiording better yields. 1

tltCS ;:l AQQ hQI. di advantage, of the processes epiployednpltill J 1Patented Sept. 20, 1960 now resides in the fact that neither the refinedproduct (paraflin oils) nor the extract (non-paraffin oils) are obtained in a sufliciently pure state and their coloration reveals theexistence of impurities that can be eliminated only by the use ofdecolorising earths. Accordingly, another purpose of the invention is toprovide means for remedying these disadvantages. 3

A further purpose of this invention is to simplify the technique ofextraction by the double solvent method, independently of the type ofthe crude mixture to be separated into its components, so as to altordaprocess and apparatus of general application.

According to one form, the present process for the extraction of ahomogeneous mixture of two liquid components by means of two solvents isprincipally characterised by the operations of: providing a refiningzone and an extraction zone, both extending in a substantially verticaldirection and each capable of bringing'about a descending flow of oneliquid in contact with a rising flow of a second liquid having aspecific gravity lower than that of the first liquid, feeding in arefining solvent at an upper part of the refining zone and producing adescending flow of the said refining solvent through the said refiningzone; feeding in an extraction solvent at a lower part of the extractionzone and producing a rising flow of the said extraction solvent throughthe said extraction zone: taking from the bottom of the refining zonethe bottom product of such zone, taking from the top of the extractionzone the top product of such zone and mixing the said bottom and topproducts with the aforementioned homogeneous liquid mixture to obtain anonhomogeneous liquid mixture; decanting by gravity the non-homogeneousmixture, separating it into a heavy phase and a light phase; feeding inthe light phase at a lower part of the refining zone to produce a risingflow of the light phase through the refining zone in refining contactwith the descending flow of the refining solvent: feeding in the heavyphase at any upper part of the extraction zone to produce a descendingflow of the heavy phase through the extraction zone in contact with therising flow of the extraction solvent; taking from the top of therefining zone a product predominantly consisting of one component of theaforementioned homogeneous mixture and of the extraction solvent, andtaking from the bottom of the extraction zone a product predominantlyconsisting of a second component of the aforementioned homogeneousmixture and of the refining solvent.

According to a further form, applied to a homogeneous mixture of mineraloils, the process according to the invention is characterised by theoperations of: providing a refining and an extraction zone, bothextending in a substantially vertical direction and each capable ofbringing about a descending flow of one liquid in contact with a risingflow of a second liquid having a specific gravity lower than that of thefirst liquid; feeding in at an upper part of the refining zone arefining solvent, capable of dissolving the non-paralfin oils, andproducing a descending flow of the said refining solvent through therefining zone; feeding in at a lower part of the extraction zone anextraction solvent capable of dissolving the parafifin oils, andproducing a rising flow of the said extraction solvent through theextraction zone; taking from the bottom of the refining zone the bottomproduct of such zone, taking from the top of the extraction zone the topproduct of such zone, and mixing the said bottom and top products withthe homogeneous mixture of parafiin oils and non-paraffin oils to obtaina non-homogeneous liquid mixture comprising a light phase and a heavyphase; decanting by gravity this non-homogeneous mixture, separating thesaid light and heavy phases; feeding refining zone in refining contactwith the descending flow of the refining solvent; feeding in the heavyphase at an upper part of the extraction zone to produce a descendingflow of the heavy phase through the extraction zone in contact with therising flow of the extraction solvent; taking from the top of therefining zone a product predominantly consisting of the parafiin oilsand of the extraction solvent; and taking from the bottom of theextraction zone a product predominantly consisting of the non-paraffinoils and of the refining solvent.

Furthermore, according to this invention, an apparatus for theextraction of a homogeneous mixture of two liquid components by means oftwo solvents is characterised by the feature of comprising incombination: a refining column and an extraction column; means in bothcolumns capable of producing an intimate contact between a liquid risingand a liquid descending through the column; means for feeding in arefining solvent at an upper part of the refining column; means forfeeding in an extraction solvent at a lower part of the extractioncolumn; a mixing receptacle in communication with a bottom zone of therefining column and with a top zone of the extraction column; means forfeeding the aforesaid homogeneous mixture into the mixing receptacle; aseparator receptacle capable of being fed from the said mixingreceptacle and having a lower zone in communication with an upper zoneof the extraction column, and an upper zone in communication with alower zone of the refining column; and means branching from the top ofthe refining column and from the bottom of the extraction column fortaking from the said columns the refined and extracted productsrespectively.

Further details of the invention will be evident from the descriptiongiven below with reference to the accompanying drawing which representsdiagrammatically one form of application of the invention for theextraction of lubricating oils.

According to the drawing, the refining column 1 and the extractioncolumn 2 which extend in a vertical direction contain means, 3 and 4,capable of producing an intimate contact between a descending liquid anda rising liquid respectively. Such means, as far as column 1 isconcerned, preferably consists of a series of plates and, as regardscolumn 2, of a large number of horizontally disposed angular sections,whereby in both columns the descending liquid may be intimately mixedwith the rising for the necessary reciprocal transfer of the extractedand refined products respectively, in a manner well-known per se in theart.

A tank 5, which contains a refining solvent well-known in the art andcomposed of equal parts of phenol and cresol, is connected by means of apipe 6, incorporating a pump 7 and a control valve 8, with an upper part9 of column 1 through which the refining solvent-aforementioned can befed into the column under volume and pres sure control.

A tank 10 containing an extension solvent comprising liquid propane isconnected by means of apipe 11, incorporating a pump 12 and a controlvalve 13, with a lower part 14 of the extraction column 2 through whichliquid propane may be fed into the column under volume and pressurecontrol.

A mixing apparatus 15, comprising a unit separate from the two columns 1and 2, is fed with crude oil through a pipe .16 which incorporates apump 17 and a control valve 18. A tube 19 leading from the bottom of therefining column 1 and incorporating a control valve 20 joins pipe 16 atsection 16a which is located between the valve 18 and the mixer 15,whereby, subject to appropriate regulation of valves 18, 20, the bottomproduct in column 1 may be brought into the mixer together with thecrude oil. Furthermore, the top product in the extraction column 2, thetop of which communicates with section 16a of pipe 16 through a tube 21,is also fed into the mixer 15.

The mixer 15 is connected by a pipe 22 with a gravity separator, ordecanter 23, of any suitable type. As is well-known in the art, aclassical form of separator comprises a bottom zone in which a heavyphase is deposited and a top zone in which a light phase is collected.The separator shown in the accompanying drawing is of a horizontal typecomprising a vertical partition 24 extending from the bottom wall up toa point at close proximity to the upper wall of the separator, so thatthe interior of the separator is subdivided into two chambers 23a, 23b,the end of the first chamber, remote from the partition 24, being fedfrom the mixer 15 through tube 22. The heavy phase collects on thebottom of chamber 23a, While the light phase passes over the partition24 and collects in chamber 23b, the separation level between the twophases being shown at 25 Therefore, considered in relation to a verticalseparator of the classical type, the chamber 23b of separator 23 may bedefined as the top zone of the separator and that part of chamber 23asituated below the level 25 may be defined as the bottom zone of theseparator.

It will further be seen from the drawing that the bottom zone ofseparator 23 is connected via pipe 26 with an upper part 27 ofextraction column 2, the pipe 26 aforesaid incorporating a pump 28 and acontrol valve 29. This valve 29 is automatically controlled by anapparatus 30 which is associated with chamber 23a of the separator andsensitive to variations in the interphase level 25. Apparatus of thiskind is Well-known in the art and does not therefore call for specificdescription.

The top zone 23b of separator 23 is connected via pipe 31 with a lowerpart 32 of the refining column 1. The pipe 31 incorporates a pump 33 anda valve 34 which is automatically controlled by an apparatus 35sensitive to the pressure obtaining in chamber 23b, in such a mannerthat valve 24 is largely opened or largely closed respectively,according to the increase or diminution, as the case may be, of thepressure in the separator 23. The extract, comprising in this casenon-paraflin oil, is taken from the bottom of the extraction column 2through a pipe 36, incorporating a control valve 37, which isautomatically controlled by an apparatus 38 associated with the bottomzone of column 2 and sensitive to variations in the level of thenon-paraffin oil which is collected in this zone of column 2.

Finally, the refined product, comprising in this case parafiin oil, istaken from the top of column 1 through a pipe 39 incorporating a controlvalve 40 which is automatically controlled by an apparatus 41 associatedwith the top zone of column 1 and sensitive to the pressure in thatzone.

As will be readily understood from this description of the apparatusaccording to the invention, the apparatus in question necessarilyoperates under super-atmospheric pressure in order to maintain thepropane in the liquid state. It will also be understood that in usingsolvents which are liquid under ordinary temperature and pressureconditions, the pressures inside the various parts of the apparatus willonly be those necessary for maintaining the individual liquid phases inmotion, and that they are therefore very substantially different fromthe pres sures required for the liquefaction of propane which may amountto as much as 25-30 atmospheres effective pressure or more.

As already stated above, the crude oil, which consists of a mutualsolution of various non-parafiin and paraflin oils, is fed through thepipe 16. As is the case with all known processes, the purpose of thisprocess is to trans.- form this solution (homogeneous mixture) into anonhomogeneous mixture of two phases and to separate the two phases fromone another by decantation. Finally, the solvents are recovered by aprocess which is known per se, but which is outside the scope of thisinvention.

In the normal operation of the apparatus here concerned, and consideringprimarily the two columns 1 and-2, it is clear that in each of thesecolumns opposite flows of two liquid phases'in contact with one anotherare stabilized, the lighter phase, comprising propane in which paraflinoils are dissolved, rising to the top of each column, and

the heavier phase comprising the phenol-cresol solvent "5 in whichnon-paraflin oils are dissolved, descending to the bottom. The bottomproduct of column 1 therefore contains a substantial proportion ofphenol-cresol solvent, while the product at the top of column 2 containsa substantial proportion of propane. These two products are 'taken fromthe respective columns through pipes 19 and 21, added to the crude'oilin pipe 16aand conveyed to the mixer 15, which as has been shown,constitutes a manifestly composed of a non-homogeneous mixture in thetwo columns operates only on a part of the crude oil, i.e. that partwhich has been pre cleansed from the unwantedcomponent. The mixer andthe separator 23 may therefore be regarded as an intermediate separationstage, outside the two columns and operating to provide through thepipes 31, 32 'a reflux for column 1, and through the pipes 26, 27 areflux for column 2. In their turn, the columns 1, 2 with pipes 19, 21respectively, produce a kind of reflux for the mixer-separator group 15,23. The interconnection between this group and the columns is regulableby means of the valves 20, 29 and 34 incorporated in the pipes 19, 2-6and 31 respectively, so that the entire process of extraction may easilybe controlled to 'aiford the most favourable results.

The table below shows the composition in kilo-grammes per'hour of thephases at the salient points of the installation, designated at the topof the individual columns by the-same reference numerals as those usedin the drawing.

Table I Operation Position Com- 16 14 9 39 36 21 19 27 32 ponent Withcrude 011 1,000 281 719 230 170 949 451 P 011 type Prnnano 2,000 1,490510 2, 500 140 1,010 1,630

.1 Phenol-Cresol solven 1,500 225 1,275 270 1, 540 1,545 265 1 Densityat 15 0.- 1.003 0. 508 1. 050 0. 576 0. 863 0. 553 0.92 0. 800 0. 595With crude Oil 1,000 342 658 235 315 893 657 oil type Prnnsme 2,0001,640 360 2, 300 230 660 1,870

...... Phenol-Cresol solvent 1, 000 350 750 290 1, 210 1, 040 460Density 0. 998 0. 508 1.050 0. 592 0. 865 0. 549 0. 916 0. 811 0. 619With crude Oil 1,000 552 448 438 390 886 942 oil type Propane"-.. 1,8001, 510 290 2,080 110 570 1,620 3 Phenol-Cresol solvent 1, 800 350 1, 450320 1, 740 1, 770 290 Density 0. 931 0. 508 1. 050 0. 619 0. 915 0. 6810. 980 0. 870 0. 631

which particles or droplets of phenol-cresol solvent with theirnon-paraflin oil content are finely dispersed among particles ordroplets of propane with their content of paraflin oils. By force ofgravity, therefore, the heavy phase containingjaf little paraffin oilwill accumulate at 40 the bottom of chamber 23a, while the light phasecontaining a little non-parafiin oil will accumulate in chamher 2312.The heavy,-or bottom, phase is then conveyed to "the top of column 2throughpipe26, while the light,

or top, phase in the separator-23 isconveyed to the bot- F tom of column1 through pipe 31. i

The light phase introduced at 32 into the refining column 1 will rise inthat column in counter-current to the descending dispersed flow ofphenol-cresol solvent,

whereby the solvent will remove from the light phase its content ofnon-paraflin oils, while, on the other hand, the propane contained inthe-light phase will keep the parafiin oils sufliciently diluted so asnot to be dissolved in the descending phase to any remarkable extent.

Finally, a product predominantly composed of par-afiin oils and propanewill be collected at the top of column 1.

The heavy phase introduced at 27 into column 2 will descend incounter-current to the rising dispersed flow of liquid propane, wherebythe latter will remove from the heavy phase its content of paraffinoils. product predominantly composed of non-paraflin oils and ofphenol-cresol solvent will be collected at the bottom of column 2.

The bottom product of column 1 is predominantly composed ofphenol-cresol solvent which carries along with it comparatively smallquantities of non-paraflin oil and propane, while the product at the topof column 2 is predominantly composed of propane which carries alongwith it comparatively small quantities of paraffin oils andphenol-cresol solvent. These two products are taken from the columnsand, as stated above, added to and vigorously remixed with the crude oilin the mixer 15 whereby the entire amount of incoming crude oil in theseparator 23 is rapidly and eificiently separated into two rough phasesFinally, a 0

i From this table it will be seen, for example, that in the case ofoperation with crude oil of type 1 there are obtained 281 liters perhour of paraffin oil leaving the topof column 1' through the pipe 39 and719 liters per through the pipe 36.

The characteristics of the crude oil, parafiin oil and non-parafiin oilrespectively in relation to the table given above will be seen from theTable II below in which the columns marked A refer to extractionaccording to the present process and the columns marked B refer to oneof the processes ordinarily employed, comprising a preliminaryasphalt-removal phase using propane, followed by extraction with phenol,while the column marked C refers to the treatment of crude oil type 3 inan ordinary extraction plant using phenol. It should be noted that thecrude oil type 3 is a vacuum-distilled oil.

In the case of all the operations conducted in the apparatus asdescribed above, all the valves shown in the diagram were so regulatedas to aiford the following internal pressures:

Atm. effective pressure At top of column 1 24.5 At bottom of column 126.0 At top of column 2 23.0 At bottom of column 2 24.0 At separator 2322.0

The temperature at which the process takes place ranges between 20 and50 C., and amounts on the average to about 35 C.

The advantages of the invention will be immediately evident uponcomparing columns B and C with columns A in Table II for each type ofcrude oil dealt with, and there is therefore no need to emphasize themfurther here.

It is also obvious that the invention is in no way restricted to theembodiment here described with reference to the accompanying drawing,but that various alternative modifications within the limits oftechnical equivalent may be applied thereto without exceeding the scopeof the even before entering the columns, In this Way each of inventionas defined in the following claims.

hour of non-paraffin oil leaving the bottom of column 2 Table IIOperation with Operation with Operation with crude oil type 1 crude oiltype 2 crude oil type 3 A B A B A 0 Crude oil:

Supply kg. per hT- 1000 1000 1000 1000 1000 1000 Density at 15 C 1.0030 1. 0030 0. 9980 0.9980 0. 9315 0. 9315 Viscosity at 210 F. incentistokes 365 365 280 280 11.35 11.35 Paraffin oil:

Supply kg. per hr 281 218 342 273 552 425 Percentage yield by weight28.1 21. 8 34. 2 27. 3 55. 2 42. 5 Density at 15 C O. 8990 0.8985 0.9050 0. 9049 0.8652 0. 8654 Viscosity at 100 F. in centl- Y okes 408 421464 473 Viscosity at 210 F. in centistokes 28. 3 28. 3 29. 4 29. 4 9. 9.35 i c ity 1n e 102 100 97 96 115 115 Viscosity index after deparatfini0n 100 98. 5 95 94 Oarbonicresid'ue acc. to Conradson (percentage 7 byWeight) 0.4 0.5 0.4 0.55 Oolor (Union)- .1 3% 5 Non-paraflin oil: ,7Supply kg. per hr. 719 782 658 727 448 575 Percentage yield by weight71. 78. 2 65. 8 721 7 44. 8 57. 5' Density at 15 C 1.052 1.036 1.0581.040 1.026 0. 9861 Viscosity at 210 F. in centistokes 1700 850 1750 93018. 1 15. 9

What I claim is:

1. An apparatus for the extraction by means of two solvents of ahomogeneous mixture of two liquid components comprising in combination:a refining column and an extraction column; means in both columns forproducing intimate contact between a liquid rising and a liquiddescending through said columns; means for feeding a refining solventinto an upper part of the refining column; means for feeding anextraction solvent into a lower part of the extraction column; a mixingreceptacle in communication with a bottom zone of the refining columnand with a top zone of the extraction column; means for feeding theaforementioned homogeneous mixture 'into'the mixing receptacle; aseparator receptacle connected to be fed from said mixing receptacle andhaving a lower zone in communication with an upper zone of theextraction column and an upper Zone in communication with a lower zoneof the refining column; and means branching from the top of the refiningcolumn andfrom the bottom of the extraction columnfor taking from thesaid columns the refined and extracted products respectively. 1

2. An apparatus for the extraction by means'of two solvents of ahomogeneous mixture of two liquid components comprising in combination:a refining column and an extraction column; means in both columns forproducing intimate contact between a liquid rising and a liquiddescending through said columns; means for feeding a refining solventinto an upper part of the refining column; means for feeding anextraction solvent into a lower part of the extraction column; a mixingreceptacle in communication with a bottom zone of the refining columnand with a top zone of the extraction column; means for feeding theaforementioned homogeneous mixture into the mixing receptacle; aseparator receptacle connected to be fed from said mixing receptacle andhaving a lower zone in communication with an upper zone of theextraction column and an upper zone in communication with a lower zoneof the refining column; valve means associated with the upper zone ofthe separator receptacle sensitive to pressure prevailing in theseparator thereby to control light phase flow from said upper zone ofthe separator to the refining column; valve means associated With theseparator receptacle sensitive to the phase separation level in thereceptacle to control heavy phase flow from the lower zone of theseparator to the extraction column, and means branching from the top ofthe refining column and from the bottom of the extraction column 'fortaking from the columns the refined and extracted products,respectively. 9

References Cited in the file of this patent UNITED STATES PATENTSLewisfi. Oct. 31, 1944

1. AN APPARATUS FOR THE EXTRACTION BY MEANS OF TWO SOLVENTS OF AHOMOGENEOUS MIXTURE OF TWO LIQUID COMPONENTS COMPRISING IN COMBINATION:A REFINING COLUMN AND AN EXTRACTION COLUMN, MEANS IN BOTH COLUMNS FORPRODUCING INTIMATE CONTACT BETWEEN A LIQUID RISING AND A LIQUIDDESCENDING THROUGH SAID COLUMNS, MEANS FOR FEEDING A REFINING SOLVENTINTO AN UPPER PART OF THE REFINING COLUMN, MEANS FOR FEEDING ANEXTRACTION SOLVENT INTO A LOWER PART OF THE EXTRACTION COLUMN, A MIXINGRECEPTACLE IN COMMUNICATION WITH A BOTTOM ZONE OF THE REFINING COLUMNAND WITH A TOP ZONE OF THE EXTRACTION COLUMN, MEANS FOR FEEDING THEAFOREMENTIONED HOMOGENEOUS MIXTURE INTO THE MIXING RECEPTACLE, ASEPARATOR RECEPTACLE CONNECTED TO BE FED FROM SAID MIXING RECEPTACLE ANDHAVING A LOWER ZONE IN COMMUNICATION WITH AN UPPER ZONE FOR THEEXTRACTION COLUMN AND AN UPPER ZONE IN COMMUNICATION WITH A LOWER ZONEOF THE REFINING COLUMN, AND MEANS BRANCHING FROM THE TOP OF THE REFININGCOLUMN AND FROM THE BOTTOM OF THE EXTRACTION COLUMN FOR TAKING FROM THESAID COLUMNS THE REFINED AND EXTRACTED PRODUCTS RESPECTIVELY.